Patterns of soil water repellency in response to coarse woody debris and fire: implications for eucalypt regeneration in dry forests

Abstract

The severity of soil water repellency (WR) is affected by fire in dry eucalypt forests in Australia. This study aimed to investigate the variability of soil WR and moisture in and around typical seedling microsites after fire: in ashbeds near coarse woody debris (CWD). Values of soil WR severity and moisture content were measured adjacent to and at multiple distances from CWD in ashbeds and in unburnt soils. Soils were measured at depths of 0 to 5 cm in 1 cm increments for 8 individual CWD samples in ashbeds. Data were analysed to determine whether WR varied significantly among soil depths and distances from CWD. In microsites subjected to a severe burn, WR differed significantly among depths but not distance from CWD. Next to CWD, soil was wettable for 1–2 cm below the surface and this wettable layer was underlain by a severely water repellent layer of at least 1 cm thickness with less repellent soil below that. In areas of less severe and no burn, surface layers were moderately to extremely water repellent. The interaction between fire and CWD and the resultant severe burn, leads to spatially restricted regions where surface soil WR is reduced, moisture accumulates and seedling establishment is promoted.